We employ a combinatorial library approach to control the shape of the silver nanostructures by regulating the structure of their seeds. Twenty-four polymers are investigated in detail with respect to their functionalities, chemical structures, molecular weights, and charges, each of which turns out to play significant roles in synthesizing high-quality silver nanoplates at room temperature in a fast manner. A mechanism depicting the exceptionally stable seed structures ‘stitched’ by polymer threads is proposed, which clearly explains the experimental observations.

We have developed a convenient and efficient colorimetric detection system for protein targets using aptamer-gold nanoparticle conjugates. We take advantage of the correlation between the catalytic properties and the exposed surface area of the nanoparticles, which is inversely proportional to the amount of the aptamer-bound protein targets. As the concentration of the protein target increases, the nanoparticle surface area becomes more masked, thus increasing the reduction time of 4-nitrophenol for the color change. We also reduce the detection time by either redesigning the aptamer sequences or regulating their density. This detection system is highly selective, discriminating the target protein even at a concentration 1000 times higher than the limit of detection (LOD). Importantly, to the best of our knowledge, the LOD with the unaided eye in this work is the lowest for a colorimetric detection system using lysozyme as a model protein (16 nM). Lysozyme in chicken egg whites is directly analyzed using our detection system, whose results are in excellent agreement with the enzyme-linked immunosorbent assay (ELISA) analysis.

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